Certain enzymes which catalyze key reactions in the biosynthesis of opium alkaloids will be investigated. These are the dehydrogenase which converts tetrahydropapaverine to papaverine, the phenol oxidases which catalyze oxidative coupling of (plus)- and (minus)-reticuline to produce aporphines (isoboldine) and hydrophenanthrenes (salutaridine), respectively, and the enzyme which promotes racemization of (plus)- reticuline. The enzymes will be isolated from the poppy latex and from the whole plant by conventional methods. The "purified" enzyme preparations will be studied with regard to physical-chemical properties, cofactors, inhibitors and stability. Chemical modifications of the natural substrates will be used to provide information about the stereospecificity and substrate specificity of the enzymes and as a means of determining the structural requirements of the active sites. This may, in turn, lead to compounds which can be converted to modified alkaloids in the enzymatic reaction or behave as competitive inhibitors of natural alkaloid biosynthesis.